Leviathan’s Program

The Society of Mind

by Marvin Minsky

Simon and Schuster, 339 pp., $19.95

Psychologists make models of the mind in order to explain what we say and do. Some particularly want to explain our abilities: how do we build a tower from toy blocks, or recognize a goldfinch? How do we manage to get across a room without hitting the furniture? Like many naive questions that lead to science, these do not have a meaning that is entirely fixed before people start to answer them. The questions seem, rather vaguely, in place when we reflect that we must learn to do these various things, that characteristic mistakes are made in trying to do them, and that our abilities to do them can be impaired through illness, injury, or age.

Yet at the outset, it is not very clear what you are asking when you ask exactly how we do such things: Is there a way in which you pick up a brick? The models of the mind that are designed to answer such questions also help to set them up, by defining what a “way” of doing something will be. They provide a topography of the mind’s functions, according to which our skills in perception, movement, or thought can be analyzed. We shall have come to understand how we do one of these familiar tasks when we see what must go on within the mind, so described, if we are to do it.

That bland and general description, however, conceals a difficulty—one large enough to make some people think that no explanation in such terms could ultimately succeed. How are we to describe what goes on in the mind? If we say that elements in the mind are able to do various relevant things—that one element recognizes a brick, for instance, and another sends the arm off to reach for it—we have only moved the problem back, from a familiar agent (the person) to a less familiar agent, the departmental chief in the mind. We shall have fallen into the homunculus fallacy, the old mistake of explaining a person’s actions in terms of actions by another (perhaps more specialized) person inside him.

If the aim is to provide a model by which all basic psychological skills can be explained, there is only one way out of this difficulty: the analysis must be carried to a level at which the mental elements themselves have no psychological capacities at all. Each of these ultimate mental items must be the kind of agent that simply, when it receives an input, sends off some output, which typically triggers other elements. The model-builder, aiming to display the structure of the mind of an agent who does have psychological abilities, will construct hierarchies and systems of such elements, specialized in the information that can affect them and in the changes that they can initiate.

It is a system of this kind that Marvin Minsky discusses in his book—or, rather, the possibility of such a system, or speculations around that possibility, since the book …

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